Chemical Composition of A193 Grade B7
B7 steel is a high-strength fastener suitable for high-temperature and high-pressure environments in American ASTM A193 / A193M “alloy steel and stainless anchor bolt materials at high temperatures” standard. This special fastener standard specifies chemical composition range of B7 grade，inspection is based on the furnace batch number, so it is suitable for high temperature and low temperature requirements and special structure types. This type of fasteners is mainly used in manufacturing industrial equipment, pipelines and wind turbines.
|ASTM A193 Grade B7 Chemical Composition|
|Carbon||Manganese, max||Phosphorus, max||Sulfur, max||Silicon||Chromium||Molybdenum|
|0.08-0.15||1.00||0.040||0.030||1.00 max||11.5 – 13.5||0.15-0.25|
ASME / ASTM, ISO898.1 and GB / T3098.1 fastener standards generally do not specifically specify chemical composition of each grade, but only give a wide range, allowing manufacturers to ensure that performance meets standard requirements. According to respective process conditions, it is selected from many blanks; delivery inspection of finished product is carried out according to production batch, and larger batch can be composed of different brands and different batches, so quality level is equivalent to (slightly higher) than ordinary standard parts.
Why Choose B7 Grade For Anchor Bolt Production
B7 steel has a wide range of chemical composition, especially carbon content. In the U.S. alloy structural steel system, B7 includes totally 6 grades such as AISI 4140, 4142, 4145, 4140H, 4142H, 4145H steel, compared with the 35CrMoA anchor bolt material grade commonly used in GB / T307721999 “alloy structural steel”, not only significantly increases carbon content, Reached the level of 42CrMoA material; and Mn content is also high.
Therefore, fastener companies must pay attention to this difference when preparing round billets. The billets of 2 types of materials cannot be used interchangeably.
Excellent Mechanical Properties of Grade B7 Steel
B7 is a high hardenability steel for quenching and tempering. Its mechanical properties, composition (especially carbon content of elemental that affects hardenability), heat treatment process and cross-sectional size are closely related. According to hardenability test, critical diameter of B7 oil quenching is 42-45 mm. Therefore, although composition range of B7 is relatively wide, in fact, it is to meet the needs of varies product specifications, and at the same time, it gives the fastener manufacturer a greater choice of round billets and heat treatment process systems.
B7 steel has a wide applicable temperature range, up to 538 ℃. After tempering, it has good low temperature toughness. Generally, brittle transition temperature is below (-50 ℃). The ASME pressure vessel code stipulates minimum temperature for B7 steel to be exempt from impact energy test is-48 ℃.
When working temperature of fastener is lower than -48 ℃, a low temperature impact energy test must be performed on B7 steel. At this time, corresponding AISI 4040H, 4142H, and 4145H steels should be selected to ensure low temperature impact performance. The chemical composition of this type of steel is basically the same of B7 steel. In addition to steel strength, main quality indicators must also include low temperature impact work tests.