Annealing temperature depends on the steel grade and on what the supplier means by “anneal.” For AISI 1045, published supplier instructions include both an 800–850°C annealing range and a 680–710°C soft-annealing range. Those values describe different process labels and should not be blended into one recommended interval. The table keeps the source and cooling instruction with every range so a reader can compare the documents without treating them as interchangeable procedures.

AISI 1045 annealing temperatures

Why the ranges differ

Kloeckner Metals describes heating AISI 1045 to 800–850°C until the temperature is uniform, then cooling in the furnace. Lucefin labels 680–710°C as soft annealing (+A), with furnace cooling and a maximum hardness of 190 HB. voestalpine HPM lists 680–710°C for annealing, slow cooling in a controlled furnace, and an annealed hardness limit of 190 HB. The two lower ranges are close and carry a softness/hardness context, while Kloeckner’s higher range is a separate supplier instruction.

“Carbon steel” alone is too broad a material identifier. AISI 1045 is a medium-carbon grade, and even that designation does not specify bar, plate, casting, initial condition, section thickness, or the acceptance property. The steel certificate and purchase specification should control the identification. The source’s process name, heating range, cooling rate, and hardness statement belong together; taking only the temperature can discard the condition that makes the result meaningful.

Worked source comparison

If a job record identifies SAE 1045 and asks for softening before machining, the Lucefin technical card is a directly named source: it lists +A soft annealing at 680–710°C and maximum 190 HB. A different record may require the Kloeckner annealing route at 800–850°C followed by furnace cooling. Before selecting either, verify that the product form and required condition match the supplier instruction. Do not pick the lower range solely because it is lower, or use the higher range as a universal substitute.

Temperature control matters through the whole workpiece, not just the furnace display. Section size, loading, furnace uniformity, atmosphere, soak time, and cooling rate affect the actual thermal cycle. The cited summaries do not provide a universal soak-time rule for every diameter. Obtain the complete current data sheet and heat treater’s qualified procedure when the part has a hardness, microstructure, distortion, or machinability requirement.

Common mistakes

The first mistake is confusing soft annealing with a full annealing cycle. They can use different temperature ranges and cooling practices. The second is copying a generic chart entry without checking whether it is intended for 1045, a particular product form, or a specific starting condition. A third is treating a stated maximum hardness as an automatic result: the complete thermal cycle and test location still matter.

The table reproduces only selected AISI 1045 guidance from Kloeckner Metals, Lucefin, and voestalpine HPM. Use the current full supplier document or a qualified heat-treatment procedure for production work.

For a controlled shop comparison, record the supplier and revision date alongside the material grade, product form, initial condition, furnace setpoint, measured load temperature, soak rule, cooling method, and hardness test location. This makes it possible to distinguish a change in the steel lot from a change in process. If a source omits soak duration, do not invent a universal “minutes per inch” value from another operation. Have the responsible heat treater specify the full cycle for the actual section and furnace load. The table’s ranges are lookup evidence; the accepted process remains the one approved for the job. Confirm the acceptance method and hardness scale before comparing results from different suppliers or test coupons. Keep the material certificate with the furnace and test records. Consult the current product sheet before adjusting a cycle.