Hardenability Bands for Carbon and Alloy H Steels J1868 Restricted

Hardenability bands for carbon and alloy h steels

This preview shows page 21 - 22 out of 61 pages.

Hardenability Bands for Carbon and Alloy H Steels J1868 Restricted Hardenability Bands for Selected Alloy Steels The place of steels in the overall UNS is documented in the standard jointly published by SAE and ASTM: SAE HS-1086/ASTM DS 56H Metals and Alloys in the Unified Numbering System. See Internet sites 4 and 5 for additional information and to acquire these standards. The new designation system permits steel manufactur- ers to modify the standard chemistry for commonly used steels to meet specific customer needs without creating an entirely new four-digit designation number. Performance requirements for press-forming, roll-forming, abrasion re- sistance, environmental corrosion resistance, cleanliness of the steel, and similar special needs can be assured more eas- ily and reliably with such a system. These situations often arise in production operations in the automotive, aerospace, appliance, construction equipment, agricultural equipment, manufacturing equipment, energy production equipment, and similar industries. A bearing steel nominally contains 1.0% carbon. Common grades are 50100, 51100, and 52100; the usual four-digit designation is replaced by five digits, indicating 100 points of carbon. Alloy Groups As indicated in Table 2–8, sulfur, phosphorus, and lead im- prove the machinability of steels and are added in signifi- cant amounts to the 11xx, 12xx, and 12Lxx grades. These grades are used for screw machine parts requiring high pro- duction rates where the resulting parts are not subjected to high stresses or wear conditions. In the other alloys, these elements are controlled to a very low level because of their adverse effects, such as increased brittleness. Nickel improves the toughness, hardenability, and cor- rosion resistance of steel and is included in most of the alloy steels. Chromium improves hardenability, wear and abra- sion resistance, and strength at elevated temperatures. In high concentrations, chromium provides significant corro- sion resistance, as discussed in the section on stainless steels. indicate the amount of carbon in the steel in hundredths of a percent. For example, when the last two digits are 20, the alloy includes approximately 0.20% carbon, and it is often said that the steel has 20 points of carbon. Small variations are allowed, say from 0.18% to 0.23%. Carbon content is part of the designation system be- cause the primary mechanical properties of strength, hard- ness, and ductility are strongly dependent on it. As carbon content increases, strength and hardness also increase dur- ing processing and heat treatment. Ductility typically de- creases so designers must balance strength and ductility when specifying a steel and its condition. It is useful to cat- egorize steels into four broad classes, low carbon, medium carbon, high carbon, and bearing steels.
Image of page 21
Image of page 22

You've reached the end of your free preview.

Want to read all 61 pages?

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture