Content MS-W. Areas of application. Product information for martensitic-phase steels

Transcription

1 Steel MS-W Product information for martensitic-phase steels Issue: December 2016, version 0 Overview of steel grades 50 Hot-rolled steel flat products Recommended applications Content 01 Areas of application 02 Available steel grades 02 Material characteristics 03 Technical features 04 Surfaces 05 Notes on applications and processing 07 Available dimensions Elongation [%] DC, DX MHZ DP CP MS-W MBW, press-hardened 500 1,000 1,500 2,000 Tensile strength [MPa] Areas of application Martensitic-phase steel MS-W is a modern, high-strength, hot-rolled multiphase steel which has a very high tensile strength of 1,180 and 1,400 MPa in thermomechanically rolled condition. In addition, a further yield increase is achieved through the work and bake-hardening effect. MS-W is particularly suitable for weight-saving production of cold-formed, crash-relevant automotive components such as side impact intrusion beams, bumper bars, filler plates, body reinforcements, and wear-exposed parts in vehicles and agricultural equipment.

2 thyssenkrupp Steel Product information MS-W Issue: December 2016, version 0 2 Available steel grades thyssenkrupp supplies the following steel grades as per the product information or the reference steel grades in accordance with the respective standards. Steel grade designations and surface refinements Surface refinements UC EG GI GA ZM AS Martensitic-phase steel Steel grade Reference grade DIN EN 10152, Reference grade VDA MS-W 900Y1180T HDT1180G1 HR900Y1180T-MS MS-W 900Y1180T Hot-rolled steel flat products Serial production for interior parts UC Uncoated EG Electrogalvanized zinc coating GI Hot-dip zinc coating GA Galvannealed ZM ZM Ecoprotect AS Aluminum-silicon coating Material characteristics Due to its selected chemical composition and its martensitic microstructure with small proportions of ferrite and/or bainite, good cold forming and welding characteristics are achieved despite the strength and wear resistance. Micrograph of MS-W 50 µm Typical microstructure of hot-rolled martensitic steels. Structural contrasting through nital etching.

3 thyssenkrupp Steel Product information MS-W Issue: December 2016, version 0 3 Technical features Chemical composition Mass fractions in ladle analysis C [%] Si [%] Mn [%] P [%] S 1) [%] Al [%] total Ti + Nb [%] Cr+Mo [%] B [%] Steel grade MS-W 900Y1180T ) To achieve good cold formability a particularly low sulfur content is set and/or favorable sulfide formation is promoted by the addition of alloying elements. Hot-rolled steel flat products Martensitic steel by thyssenkrupp is a fully killed fine grain steel. For additional formation of a finely granular structure and/or nitrogen fixation, Nb, Ti and B are used individually or added in combination as required. Mechanical properties Yield strength Tensile strength Elongation Test direction in rolling direction R p0.2 [MPa] R m [MPa] A [%] min. A 80 [%] min. Steel grade MS-W 900Y1180T 900 1,180 1,180 1, Hot-rolled steel flat products R p0.2 Proof strength at 0.2% plastic elongation R m Tensile strength A Percentage elongation after fracture using a proportional specimen with L 0 = 5.65 S 0 for sheet thicknesses 3.0 mm Percentage elongation after fracture using a specimen with gauge length L 0 = 80 mm for sheet thicknesses < 3.0 mm A 80 Martensitic steel is not suitable for heat treatment. Temperatures above 250 C can impact the mechanical properties, thus causing them to drop below the guaranteed values.

4 thyssenkrupp Steel Product information MS-W Issue: December 2016, version 0 4 Surfaces Surface refinements, electrogalvanized zinc coating Specification Nominal coating on each side of single spot sample Coating on each side of single spot sample Mass [g/m 2 ] Thickness [μm] Mass [g/m 2 ] Thickness [μm] Electrogalvanized zinc coating Designation EG25 / 25 DIN EN EG18 VDA EG50 / 50 DIN EN EG29 VDA EG75 / 75 DIN EN EG53 VDA EG100 / 100 DIN EN EG70 VDA On request, material can be supplied with zinc coating on one side or on both sides with different coating weights. Surface finishes and surface qualities Finish type Surface quality Products Electrolytically zinc coated flat products Electrogalvanized zinc coating A Normal surface U Unexposed (interior parts) A as per DIN EN U as per VDA Surface treatments Type of surface treatment O Oiled UC EG GI GA ZM AS Serial production UC Uncoated EG Electrogalvanized zinc coating GI Hot-dip zinc coating GA Galvannealed ZM ZM Ecoprotect AS Aluminum-silicon coating

5 thyssenkrupp Steel Product information MS-W Issue: December 2016, version 0 5 Notes on applications and processing Forming Hot-rolled martensitic steel is particularly suitable for crashrelevant parts, such as side impact intrusion beams and bumper bars. Working is often implemented as crash forming, that is, without a blank holder in a forming stage, or by folding or bending operations. Calibration should be integrated to enable specific, localized plasticization, in order to improve the dimensional accuracy of the worked components. Suitability for roll forming is guaranteed. Special attention must be paid to the design of the cutting and forming tools. Tool requirements are exacting, especially in cutting. In addition to a sufficient hardness of > 60HRC, it is important to select suitable tool materials to simultaneously ensure high ductility, thus preventing premature breaking of the cutting edges. By means of specific round ing of the cutting edge in the order of about 50 μm, the edge strength of the tools can be optimized. The cutting gap must be designed to take the material thickness into account and should be (as a guideline) 12% of the sheet thickness. A sufficient supporting hardness must be achieved for the forming tools. A segmented structure of the forming tools is common today. In highly stressed areas, the use of high speed steels may be necessary. These include or equivalent materials produced by sintering. In addition, tool coat ings such as CVD (TiC-TiN coating) can minimize tool wear. The intended presses should have high pressing and hold-down force potentials. As a guideline, the tensile strength level should be considered here, compared with known materials. Upstream straightening equipment must also be designed accordingly. Increasing strength naturally limits the formability of ultra-highstrength materials. When designing components, particular attention must therefore also be paid to thickness reduction, surface strain and the forming limit curve. In all cases forming simulation is also recommended. The required characteristic values and a guide including detailed processing information are available on request. Processing instructions for joining Martensitic steels are suitable for welding in both same-grade joints and hybrid joints with other common steel grades. The precondition is welding parameters matched to the material. Resistance spot welding For spot welding the same equipment can basically be used as for welding unalloyed deep-drawing steels. However, the electrode forces must be increased compared to steels of lower strength in order to achieve a large welding zone. Stable and rigid welding rods with large power reserves are therefore recommended for martensitic steels; this may also offer advantages in case of larger sheet thicknesses or engineering fit issues. Extending the welding time has a positive effect on the welding zone; for this reason, medium to long welding times are recommended for spot welding. Similarly, the use of multipulse welding as per SEP can have a favorable effect on the width of the welding zone. Compared to lower-strength steels, martensitic steel has lower electrical conductivities; lower welding currents thus tend to be required for spot welding electrodes with the same force. In resistance spot welding of galvanized sheets, the welding currents must be increased due to the higher conductivity of the coating compared with the base material (substrate). In addition to this, increasing the electrode force and welding time has a favorable effect on the welding zone. Apart from the sheet type, surface and thickness combination, other factors e.g., the type of electrode used, play an important role in determining optimum joining parameters. The relationships shown in the figure should therefore only be understood as examples.

6 thyssenkrupp Steel Product information MS-W Issue: December 2016, version 0 6 Typical properties of a resistance spot weld Plate thickness Welding zone ΔI Cross tensile strength for d w min Shear tensile strength for d w min Mean hardness HV 0.1 [mm] [ka] [kn] [kn] Base material Weld nugget Steel grade HX340LAD+Z MS-W 900Y1180T Test results as per SEP Hot-rolled strip Cold-rolled strip t Sheet thickness of test specimens d w min Welding spot diameter of 4 t MHZ 340 Hardness profile of the weld nugget in a MS-W 900Y1180T 500 Ø420 Ø420 MS-W 900Y1180T Ø420 Hardness HV WEZ 1 WEZ 2 Good weld nugget formation Distance [mm] 15 Normal hardness drop in the heat-affected zone. MIG arc brazing Information sheet DVS Arc brazing describes brazing of steels up to a tensile strength of approximately 500 MPa. As the material described here is above this tensile strength, it is advisable to check the component-specific suitability of brazing. Martensitic steel exhibits an even higher crash deformation resistance than complex-phase steels. It is thus more suitable for side impact intrusion beams, bumpers and reinforcement parts that are designed in particular to prevent a component group buckling under crash load. Fatigue strength and crash performance Martensitic steel exhibits greater structural durability. In terms of stress-strain curve characteristics the steel is superior to dual-phase and austenitic steels. However, in case of excessive elongation, that is, in case of misuse load, its behavior is more sensitive than that of complex-phase steels.

7 thyssenkrupp Steel Product information MS-W Issue: December 2016, version 0 7 Available dimensions MS-W 900Y1180T Width [mm] Thickness [mm] ,000 1,000 1,050 1,050 1,100 1,100 1,150 1,150 1,200 1,200 1,250 1,250 1,300 1,300 1,350 1,350 1,400 1,400 1,450 1,450 1,500 1,500 1,550 1,550 1,600 1,600 1,650 1,650 1,700 1,700 1,750 1,750 1,800 1,800 1,850 1,850 1,900 1,900 1,950 1,950 2,000 2,000 2,050 2,050 2,100 2,100 EG Electrogalvanized zinc coating EG trimmed Uncoated with mill edge For interior parts Typical dimensions for automotive customers. Restrictions may apply to steel grades as per VDA Further dimensions on request.

8 thyssenkrupp Steel Product information MS-W Issue: December 2016, version 0 8 Special mill grades are supplied subject to the special conditions of thyssenkrupp. Other delivery conditions not specified here will be based on the applicable specifications. The specifications used will be those valid on the date of issue of this product information brochure. thyssenkrupp Steel Europe AG, Kaiser-Wilhelm-Straße 100, Duisburg, Germany Postal address: Duisburg, Germany, T: , F: info.steel@thyssenkrupp.com General information All statements as to the properties or utilization of the materials and products mentioned in this brochure are for the purpose of description only. Guarantees in respect of the existence of certain properties or utilization of the material mentioned are only valid if agreed in writing. Subject to technical changes without notice. Reprints, even extracts, only with the permission of thyssenkrupp Steel Europe AG. The latest information can be found on the Internet: