Fasteners, bearings, gears, springs, molds and dies are the basic parts of mechanical manufacturing, which directly affect the quality and reliability of machinery. Fasteners, bearings, gears, springs, molds and other service environment is different, the quality of the material requirements are also different.
Fasteners steel
Fasteners is the largest application of basic parts, fasteners with steel covers almost all steel categories, including cold heading steel, alloy structural steel, stainless steel, heat-resistant steel, etc., the standard strength level in the range of 400 MPa ~ 1200 MPa. Typical steel grades for the fasteners are MLO8A1, SWRCH22A, SWRCH35K, 10B21, 40Cr, SCM435, SCM440, 40CrNiMo, SNB16, 304, 316, 430, PH13-8Mo. Fasteners are usually manufactured using the cold heading process, which requires steel with good cold heading properties. Depending on the application scenario, steel for fasteners also needs to be resistant to fatigue damage, delayed fracture, corrosion, high and low temperatures. Low-cost competition for fasteners has prompted MnB steel to replace CrMo steel in large quantities. At present, mechanical lightweight requirements 14.9 and above high-strength fasteners, in addition to the production process issues need to be resolved, but also to pay attention to delayed fracture and fatigue damage and other issues.
Bearing steel
There are two main forms of bearing damage, namely contact fatigue damage and wear damage. Because of the need to withstand high contact stress (generally up to 2 Gipa ~ 5 Gipa), multiple cycles of contact fatigue stress and in the sliding wear of the working environment, bearing steel needs to have a high hardness, high fatigue performance, high reliability. For bearings working under special conditions, must also have impact resistance, high DN value, high and low temperature resistance, anti-corrosion and anti-magnetic properties.
General bearing steel is divided into 4 categories: high carbon chromium bearing steel, carburized bearing steel, stainless bearing steel and high temperature bearing steel. Bearing steel quality indicators are mainly oxygen content, titanium content, non-metallic inclusions, carbide segregation and so on. Typical bearing steel GCr15, M50. High-carbon chromium bearing steel GCr15 generally adopts the ultra-pure smelting method of iron converter + furnace refining + continuous casting, and the oxygen content can be controlled to be no more than 4ppm (ppm is one millionth). The contact fatigue life L10 of GCr15 can reach 107~108 orders of magnitude. Various strength manufacturers are developing materials for high-speed rail bearings, electric vehicle bearings, wind power bearings, machine tool bearings, aviation bearings and so on.
Gear steel
Gear steel is mainly surface carburizing low to medium carbon alloy structural steel, typical steel 20CrMnTi, CrMn, CrMo, CrNiMo series, etc., and a small number of medium carbon alloy structural steel, a very small number of aviation gear steel 9310, M50NiL, 8620, etc..
The main quality indicators of gear steel are hardenability, purity, grain size, banding organization. Gear steel produced using high-turn process can achieve: oxygen content ≤ 12ppm; A, B, C, D class of coarse system, fine system and Ds inclusions 9 sum ≤ 6.0, banded organization is not more than 2 levels, HRC ≤ 4HRC.
Spring steel
Spring steel is mainly medium-high carbon alloy structural steel, typical steel is 65Mn, 60Si2Mn, 50CrV, 55SiCr, etc. In addition, there are a small number of corrosion-resistant stainless spring steel.
The control of inclusions in spring steel is the key link to ensure the quality of spring steel. Reduce inclusions in spring steel, the key is to control the oxygen content and acid-soluble aluminum content. The use of high-turn process production of spring steel can be realized: oxygen content of not more than 10 ppm, A, B, C, D class of coarse system, fine system and Ds inclusions 9 sum ≤ 4.0. Some spring steel species such as valve springs, clutch springs (2300 MPa), tailgate springs (2300 MPa) steel wire quality and stability needs to be improved. 2100 MPa level spiral suspension spring steel coils are also being developed
Mold steel
Commonly used mold steel Cr8Mo2VSi (DC53), A2, A8, D2, S7, H11, H13. At present, the development of high corrosion-resistant plastic mold steel, high-temperature aviation mold materials, high thermal conductivity mold steel, high wear-resistant and high toughness cold-worked mold steel, powder metallurgy mold materials.
