A quality inspector at a fabrication shop rejected a shipment of A572 Grade 50 plate because the MTR showed a carbon equivalent (CE) of 0.48. The specification limit for the grade is 0.45. The service center had shipped material that was in-spec for chemistry and mechanical properties but out-of-spec for weldability. The MTR contained all the information needed to catch this before shipment. Nobody at the service center had checked.
What an MTR Contains
A mill test report (also called a certified material test report, CMTR, or mill cert) documents the chemical composition and mechanical properties of a specific heat of steel. Every MTR should include the mill name and location, the heat number (the unique identifier for the batch of steel produced from a single furnace charge), the product specification (ASTM A36, A572 Gr 50, etc.), the chemical analysis (percentages of carbon, manganese, phosphorus, sulfur, silicon, and other elements), the mechanical test results (yield strength, tensile strength, elongation, and sometimes Charpy impact values), and the product dimensions (thickness, width, or diameter).
The heat number is the critical traceability link. It connects a specific coil, plate, or bar on your warehouse floor to a specific batch of steel produced at a specific mill on a specific date. If a quality problem surfaces downstream, the heat number traces every piece of affected material through the supply chain.
Chemical Composition: What to Check
Every ASTM specification defines maximum (and sometimes minimum) limits for key elements. For carbon steel, the primary elements to verify are carbon (C, which determines hardness and weldability), manganese (Mn, which affects strength and hardenability), phosphorus (P, an impurity that must stay below maximum limits), and sulfur (S, another impurity with strict limits). For higher-grade specifications, additional elements matter: vanadium, columbium (niobium), and nitrogen for HSLA grades, chromium and molybdenum for alloy grades.
The most common chemical issue for service centers is carbon content. Higher carbon means higher strength but reduced weldability. If your customer plans to weld the material (and most fabricators do), verify that the carbon content and carbon equivalent are within the limits their welding procedure requires. Many fabricators specify a maximum CE of 0.45 for structural steel that will be welded without preheat.
Mechanical Properties: What Matters
Yield strength is the stress at which the steel begins to permanently deform. Tensile strength is the maximum stress before failure. Elongation measures ductility (how much the steel stretches before breaking). For structural applications, yield strength is the design basis. For forming applications, elongation is often more important because it determines how much the material can bend without cracking.
Check that the actual test values meet the minimum requirements for the specified grade. A36 requires minimum 36 ksi yield and 58-80 ksi tensile. A572 Grade 50 requires minimum 50 ksi yield and 65 ksi minimum tensile. Material that meets A36 but not A572 Grade 50 cannot be sold as Grade 50, even if it looks identical.
Common MTR Problems
Missing MTRs are the most frequent issue. You receive material from the mill without the corresponding MTR, or the MTR does not match the specific coils or plates received. Establish a process that verifies MTR receipt against every incoming shipment before the material enters available inventory.
Incorrect MTR assignments happen when material is split, processed, or transferred and the MTR does not follow accurately. If you slit a master coil into five mults, each mult should carry the original MTR traceability. If you sell partial quantities off a coil, the remaining material must retain its MTR link. Losing traceability between physical material and its MTR creates a documentation gap that surfaces during customer audits.
Foreign-language MTRs from import material sometimes lack the format that domestic customers expect. Translate and reformat if necessary, but never alter the actual test data. Your role is to pass through the mill's certified data, not to generate your own.