HEAT TREAT BULLETIN BULLETIN REVIEW

Transcription

1 Bulletin No. 7 ISO 9001 Registered HEAT TREAT BULLETIN BULLETIN REVIEW

2 BULLETIN REVIEW In an effort to improve our product and service, East-Lind Heat Treat has issued six bulletins over the past three years. Each bulletin detailed specific heat treat procedures and common problems associated with the heat treatment of metals (both ferrous and non-ferrous). These bulletins have been well received. At this point we would like to review some of the major topics of these bulletins to help reinforce them. We will indicate where our suggestions have had a positive effect for our customers and East-Lind Heat Treat as well. In some areas, there still seems to be a bit of confusion. We will attempt to clarify these areas. BULLETIN #1 DETERMINING HARDNESS RANGES FOR CARBON & ALLOY STEELS Bulletin #1 is devoted to the specification of hardness requirements for the major groups of tool steels; i.e. water hardening, oil hardening, and air hardening. All three grades should have a specified range of hardness of RC in stress-induced applications. In low or non-stress applications, a hardness of RC is recommended. A specified hardness above RC 61 should be reserved for the various high-speed steels. An entirely different group of alloy steels are referred to as specialty steels. These steels are also water, oil or air quenched. However, the desired hardness of these steels differs from the tool steels due to their chemistry. Specialty steels include the H series, the S series, the M & T types of high speed steels, and various alloy grades 6150, 4140, etc. The high speed steels (T-1 to T-15 and M-1 to M-42) have a tempered hardness in the range of RC 61 to RC 70 depending on the grade. The H series ( hot work steels) are steels used to make tools and dies that perform in service while heated to elevated temperatures (forging dies, extrusion dies, etc.). The hardness range used for these steels is RC The as-quenched hardness of the H steels is no more than RC A recommended temper of 1000 F to 1100 F brings the hardness into the RC range. A specified hardness above RC 50 tends to leave these steels brittle. The S series ( shock steels) involve water or oil hardening grades. These steels are used where repeated shock loading is experienced in service (such as chisels). The tempered hardness range of these steels, as a group, is RC Alloys such as 4140, 6150, 4150, etc. will develop an as-quenched hardness of RC depending on the mass effect. The mass effect dictates that the larger or thicker the steel section, the slower the quench rate and thus the lower the overall hardness.

3 These particular alloys have more than.30% of carbon and significant alloy elements, such as chromium. Therefore, these steels should not be surface hardened by carburization to attain a higher hardness. These are straight (through) hardening steels. We have focused primarily on the maximum hardness ranges here, but the proper range of hardness for any steel is relative to the grade and the application involved. Since the publication of bulletin #1, we have seen a significant reduction in requests for unreasonable hardness requirements - those above RC 61. But there will always be a notion somewhere that harder is better. You now know that this is not always true. BULLETIN #2 PROPER STEEL SELECTION AND DESIGN PAVE THE WAY FOR SOUND TOOL & DETAILS Bulletin #2 dealt with the proper steel selection for a particular application; proper heat treatment; proper final grinding and good, sound design. The selection of the proper steel for a particular application has not been much of a problem since most details use a type of steel that has been specified for many years. What is still an on-going problem for the heat treater is design faults which account for more than 90% of heat treat failures. These faults are: o Heavy sections adjacent to light sections; o Holes too close together or holes too close to an edge; o And most significantly, sharp inside corners. An analysis of nearly all sharp inside corner failures indicate that the presence of this design fault was not necessary. Sharp inside corners always concentrate quenching and service stresses. Any time that the stress concentration exceeds the cohesive strength of the steel, the steel will crack at the sharp corner. Of all the improvements that we have seen since the introduction of these bulletins, the problem of sharp inside corners still exist. The elimination of sharp inside corners on parts that are quench hardened, whether in oil, water or air, will save countless details from the scrap bin. BULLETIN #3 DISTORTION DURING HEAT TREATMENT & SEGREGATION CRACKS IN PARTS MADE FROM PLATE STEEL PRODUCTS Bulletin #3 addressed the topics of distortion and segregation cracks in quenching and tempering.

4 There is not much to add to the information in this bulletin. Distortion a change in size (length or width, holes that drift apart or close in) and/or shape (warpage) are inherent to the heat treat process and for the most part are still beyond the heat treater s ability to control. The distortion that causes bending, bowing, twisting or cambering is usually corrected by peening or applying heat, pressure or both to achieve the correct amount of straightness. Size change can only be accounted for by leaving sufficient grind stock. Segregation cracks, as described on pages 3 and 4 of the bulletin, are still with us on occasion. As long as bar stock continues to be made from plate steel products, segregation cracks will be a problem from time to time. BULLETIN #4 CASE HARDENING OF STEEL COMPONENTS & STRAIGHTENING Bulletin #4 concerns case hardening (carburizing), the addition of carbon to a steel of lesser carbon content. Since the bulletin was issued, we have seen a decided improvement in the understanding of the nature and application of the carburizing procedure. As explained in the bulletin, we no longer carburize plain carbon steels having carbon content above.30% carbon or any alloy steel which has a carbon above.30% and additional alloys of chromium, nickel, molybdenum, etc. (4140, 4150, 6150, 1060, etc.). These are not carburizing grades and they are not recommended for case hardening. If a hard surface and soft, tough core are required, these grades are well suited for flame or induction hardening. When a detail is designed to be case hardened, special consideration should be given to any area which would develop more case depth than core thickness. An area which is carburized leaving little or no core will become brittle and will usually crack during the quench hardening procedure. Details of such design should be made from through hardening steels where carburizing is not necessary. Regarding straightening, Bulletin #4 defines peening as a mechanical means of straightening using a hammer that has a brazed cemented carbide wedge. This carbide tipped hammer diverts the surface stresses to another area creating a flattening of the distorted area. When a hand held peening hammer is used, the peen marks can be so deep that they will not clean up in final grinding. At East-Lind, we have replaced hand held peening hammers in most cases with pneumatic hammers. The peen marks with this type of peening is much lighter and less penetrating into the surface and easier to clean up in the final grinding operation. However, sufficient grind stock is still required.

5 BULLETIN #5 HELP YOUR HEAT TREATER HELP YOU In Bulletin #5 we asked you to assist us in helping you by identifying small parts to ensure less confusion among parts of similar size but a different configuration. More of you are sketching the shape of the part on your incoming order or you are sending a print copy with the order. This has simplified our inspection operations and has resulted in a decrease in lost or misidentified parts for our customers. We can still use a little help. When filling out your heat treat work order, don t take short cuts. Be clear, write legibly and include as much information as possible, including customer ID#, phone# and contact person in case we have any questions before processing the job. When you call in to check on a job or send someone to pick-up your work, we can assist you better if you can provide us the following information: Your company name Date the job came in to us Type of steel Size and shape description Process requested (hardening, carburizing, flame hardening, etc.) Bulletin #5 also discussed the importance of allowing us enough time to produce a properly heat treated part. All heat treating procedures require a minimum amount of time for: Pre-heating Solutioning Carburizing Quenching (Hardening) Tempering Straightening when required Cleaning- sand blasting, washing clay & salt removal Final Inspection If you ask us to skip or accelerate any of these steps, we cannot guarantee that the heat treated part will meet your requirements. BULLETIN #6 DESIGN FAULTS RELATIVE TO QUENCH HARDENING Bulletin #6 again emphasizes the danger of design faults especially sharp, inside corners that allows for the build-up of stresses which may well cause a fracture during the hardening procedure. SUMMARY Again, we are pleased with the response and comments that we have received since the publication of these six bulletins. Feel free to make copies for others in your plant or contact us for additional copies or if you are missing any of them. Bulletins are also available in our shipping & receiving department as well as our website We suggest putting them in ringed binders for future reference. More bulletins will be sent from time to time. If there is a topic that you would like us to include in future bulletins, please contact us.

6 Written and published by East-Lind Heat Treat, Inc. for exclusive use by its customers. All technical questions regarding this bulletin may be directed to Dale Greer, Quality Manager. To order additional copies of this or other bulletins please contact our office at (248) EAST-LIND HEAT TREAT, INC Dequindre Rd. Madison Heights, MI ATTN.: PLANT MANAGER IMPORTANT INFORMATION